House Speaker Paul Ryan of Wis. speaks during his weekly news conference on Capitol Hill on Thursday, May 19. Nearly every House Democrat has signed a letter calling on Ryan to shut down the special investigative committee probing the fetal tissue industry. (AP Photo/Andrew Harnik)

All but a handful of House Democrats are calling on Speaker Paul D. Ryan to disband the special committee established last year to probe connections between abortion providers and medical researchers, accusing the panel of “continued abuses which jeopardize the integrity of the House and the safety of Americans.”

The letter represents a new salvo in the partisan warfare over the Select Investigative Panel established in October in response to a series of undercover videos produced by anti-abortion activists. All but two Democrats voted against creating the panel, and Democratic members of the committee have called since then on several occasions for its dissolution.

The new letter, signed by 181 of 188 House Democrats, raises the protests to a new level, asking Ryan (R-Wis.) for a written response to their accusations of harassment, intimidation and McCarthyism on the part of the panel’s Republican members and staff.

“Speaker Ryan is the speaker of the whole House,” said Rep. Diana DeGette (D-Colo.), a Select Panel member. “It’s job of the speaker to maintain some level of decorum in the House, and if the speaker finds out that a select committee that has been appointed by his predecessor and supported by him is on a partisan witchhunt, he needs to stop it.”

DeGette and Rep. Louise Slaughter (D-N.Y.), who are co-chairs of the Congressional Pro-Choice Caucus, gathered support for the letter, along with Rep. Jan Schakowsky (D-Ill.), the ranking Democrat on Select Panel.

In his nearly six months as speaker, Ryan has quietly expressed support for the panel and its chairwoman, Rep. Marsha Blackburn (R-Tenn.), as it has issued subpoenas to abortion providers, research institutions and other entities involved in fetal-tissue procurement.

A spokeswoman for Ryan responded to a previous call for the panel’s demise with a brief statement of support: “Speaker Ryan supports the Select Committee’s continued efforts to protect infant lives.” AshLee Strong, the spokeswoman, said Tuesday her previous comment applied to the new letter as well.

DeGette said she tried to raise the matter directly with Ryan at a charity event both attended last week: “He said, ‘Now is not the time to talk about this.'” The letter is asking Ryan for a written response by June 6, and DeGette said she is seeking a meeting with Ryan about the panel.

Earlier this month, House Minority Leader Nancy Pelosi (D-Calif.) said the panel was “engaged in abuses that have not been seen on Capitol Hill since the days of Joseph McCarthy,” referencing the disgraced former senator who waged a scorched-earth search for communists in the federal government. The panel’s requests for names of researchers and other personnel, Pelosi and other Democrats say, amounts to a similar effort at political intimidation.

“To this day, the Panel still lacks credible evidence to support its case that any federal laws were broken,” the new letter reads. “Yet the Chair and majority staff continue to harass individuals, researchers, clinics, and health care facilities, issuing a total of 35 subpoenas so far, often without reaching out to the subject of the subpoena to ask for voluntary compliance first or without giving subjects sufficient time to comply. Congress simply has no business ‘prosecuting’ these unfounded allegations.”

The panel issued subpoenas this month targeting LeRoy Carhart, a late-term abortion specialist who has long been been a target of antiabortion activists, Carhart’s clinic in Germantown, Md., and various entities involved in the response to the 2013 death of a 29-year-old woman at the clinic. Three Maryland state agencies found no wrongdoing in the incident.

The panel has thus far held two public hearings. The first sought to cast doubt on the ethics and efficacy of fetal tissue research; the second probed whether abortion clinics have illegally profited through their relationships with medical researcher.

Responding to a previous call for the panel’s disbanding, Blackburn spokesman Mike Reynard said the panel is focused on determining whether human fetal tissue is being sold on contravention of federal law: “While the majority members of the Panel are busy pursuing those records, all that can be heard from the Democrats is the same old tired rhetoric designed to distract from getting to the truth.”

DeGette said the panel’s conduct has become a “public safety issue,” citing the November shooting at a Planned Parenthood clinic in Colorado, which left three dead and nine injured at the hands of a mentally ill man who made reference to “baby parts” in interviews with authorities.

“Despite this horrific event, the same inflammatory language has been used repeatedly during Panel hearings, in communications with the press, and in other documents,” the letter reads, before imploring Ryan to step in: “The onus is on you to put an end to this witch hunt. You cannot continue to turn a blind eye to the serious risks presented by the Panel and still claim to fulfill your responsibilities as Speaker.”

This post was updated at 12:40 p.m. and 6:20 p.m. with additional signers.